GHSA-533c-2vh9-4r86 is a medium-severity (CVSS 4.8) Code Injection vulnerability in decidim-core. O3 Security confirms whether GHSA-533c-2vh9-4r86 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Decidim: HTML content blocks allow stored script execution
Real-World Exposure
decidim-core💎decidim-core💎decidim-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Description
A privileged admin user who can edit an affected landing page can store arbitrary HTML/JavaScript in an HTML block, and the public page renders it with html_safe and no output escaping.
Technical description
This issue lets any admin who can edit an affected landing page store arbitrary HTML and JavaScript in an HTML block. The block is then rendered back through Decidim::ContentBlocks::HtmlCell#html_content without a sanitization boundary, so the script executes later in visitor's browsers.
Impact
- A user with landing-page editing rights for an affected scope can persist JavaScript that executes in visitor's browsers on that page.
- Because exploitation already requires privileged administrative access, the practical risk is lower than a participant-controlled or unauthenticated stored XSS. It still creates a browser-execution primitive in a trusted admin-editable surface.
Patches
See https://github.com/decidim/decidim/pull/16451
Workarounds
Do not give admin permissions to non-trustful users.
Reference
Stored XSS
Credits
This issue was discovered in a security audit organized by the Decidim Association and made by Radically Open Security against Decidim financed by NGI.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | decidim-core | all versions | 0.30.9 |
| 💎RubyGems | decidim-core | ≥ 0.31.0.rc1&&< 0.31.5 | 0.31.5 |
| 💎RubyGems | decidim-core | ≥ 0.32.0.rc1&&< 0.32.0 | 0.32.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for decidim-core. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update decidim-core to 0.30.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-533c-2vh9-4r86 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-533c-2vh9-4r86 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-533c-2vh9-4r86. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-533c-2vh9-4r86 in your dependencies?
O3 detects GHSA-533c-2vh9-4r86 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.